Antiphons sung before and after the Magnificat at vespers on the seven days before Christmas. The texts are of unknown origin and date at least from the ninth century. Each antiphon begins with the letter "O" and a name or attribute of God from the Hebrew Scriptures: O Sapientia, "O Wisdom"; O Adonai, "O Sacred Lord"; O Radix Jesse, "O Root of Jesse"; O Clavis David, "O Key of David"; O Oriens, "O Rising Sun"; O Rex gentium, "O King of nations"; and O Emmanuel, "O Emmanuel." In the Roman rite the antiphons are sung from Dec. 17-23, but in the medieval Sarum use they began on Dec. 16, adding on Dec. 23, O Virgo virginum (O Virgin of virgins). The Great O Antiphons have been adapted as a popular Advent hymn, "O come, O come, Emmanuel" (Hymn 56), whose verses may be used as antiphons for the Magnificat on the appropriate days.
Great O Antiphons of Advent
Glossary definitions provided courtesy of Church Publishing Incorporated, New York, NY,(All Rights reserved) from "An Episcopal Dictionary of the Church, A User Friendly Reference for Episcopalians," Don S. Armentrout and Robert Boak Slocum, editors.